A performance improving technology related to data transfer by a bridge device has hitherto existed. The following are known as one example of the bridge device to which the performance improving technology is applied. The bridge device is configured by including an MPU (Micro Processing Unit), an interrupt controller and a data buffer. The bridge device establishes a connection between a communication controller and a memory controller that accesses a NAND flash memory. The bridge device, which includes a built-in MPU and a built-in interrupt controller, not only simply establishes a connection between bus segments but also performs a communication process such as packetizing and depacketizing, and controls the memory controller and the communication controller. Thus, the bridge device is configured to get capable of taking itself a processing burden imposed on a CPU (Central Processing Unit) which controls the bridge device, whereby the processing load on the CPU is reduced. Data transfer performance is thereby improved. Nevertheless, such problems exist that an interrupt occurs on a packet-by-packet basis, a software processing load on the MPU is high, and a sufficient throughput is not obtained.
Moreover, a system is known as another technology different from the above, the system including an interrupt proxy processing unit to improve the data transfer performance by reducing a load of a DMA (Direct Memory Access) transfer process and a load of an interrupt process with which the CPU is burdened. Nonetheless, this system has a problem of not exhibiting sufficient effects in improving the transfer performance with respect to the file transfer. A reason why so is that the file transfer process involves a process related to the file system, but it is impossible to improve the performance of the relevant part even by using this technology. Accordingly, if the file system process turns out to be a factor for deteriorating the performance, it is unfeasible to sufficiently enhance the data transfer performance of the file transfer between the storage and the network.